Biscuit joinery requires a specialised tool, but it also provides a quick, simple joint that is strong enough for most applications. Here's how a biscuit joiner works, and a few applications when you might use one.
Dovetail joints are, in my opinion, the prettiest of joinery techniques. They provide incredibly strong joints that, if done correctly, don't even need glue to hold them together. However, they also require much more skill and precision to create than other joinery methods.